Enhanced channel interleaving for optimized data throughput

ABSTRACT

In a transmission scheme wherein multi-slot packet transmissions to a remote station can be terminated by an acknowledgment signal from the remote station, code symbols can be efficiently packed over the multi-slot packet so that the remote station can easily decode the data payload of the multi-slot packet by decoding only a portion of the multi-slot packet. Hence, the remote station can signal for the early termination of the multi-slot packet transmission, which thereby increases the data throughput of the system.

CLAIM OF PRIORITY UNDER 35 U.S.C. § 120

This application is a continuation of, and claims priority to, U.S. Ser.No. 14/272,852 filed May 8, 2014, entitled “Enhanced ChannelInterleaving For Optimized Data Throughput,” which is a continuation ofand claims priority to U.S. Ser. No. 13/013,710 filed Jan. 25, 2011, nowgranted as U.S. Pat. No. 8,873,534 on Oct. 28, 2014, entitled “EnhancedChannel Interleaving For Optimized Data Throughput,” which is acontinuation of and claims priority to U.S. Ser. No. 11/332,722 filedJan. 12, 2006, now granted as U.S. Pat. No. 7,953,062 on May 31, 2011,entitled “Enhanced Channel Interleaving For Optimized Data Throughput,”which is a continuation of and claims priority to U.S. Ser. No.09/863,196 filed May 22, 2001, now granted as U.S. Pat. No. 6,987,778 onJan. 17, 2006, and entitled “Enhanced Channel Interleaving for OptimizedData Throughput,” each of which is assigned to the assignee hereof andhereby expressly incorporated by reference herein.

BACKGROUND

Field of the Invention

The present invention relates to data communication. More particularly,the present invention relates to optimizing the data throughput of awireless communication system.

Background

The field of wireless communications has many applications including,e.g., cordless telephones, paging, wireless local loops, personaldigital assistants (PDAs), Internet telephony, and satellitecommunication systems. A particularly important application is cellulartelephone systems for mobile subscribers. (As used herein, the term“cellular” systems encompass both cellular and personal communicationsservices (PCS) frequencies.) Various over-the-air interfaces have beendeveloped for such cellular telephone systems including, e.g., frequencydivision multiple access (FDMA), time division multiple access (TDMA),and code division multiple access (CDMA). In connection therewith,various domestic and international standards have been establishedincluding, e.g., Advanced Mobile Phone Service (AMPS), Global System forMobile (GSM), and Interim Standard 95 (IS-95). In particular, IS-95 andits derivatives, IS-95A, IS-95B, ANSI J-STD-008 (often referred tocollectively herein as IS-95), and proposed high-data-rate systems fordata, etc. are promulgated by the Telecommunication Industry Association(TIA), the International Telecommunications Union (ITU), and other wellknown standards bodies.

Cellular telephone systems configured in accordance with the use of theIS-95 standard employ CDMA signal processing techniques to providehighly efficient and robust cellular telephone service. Exemplarycellular telephone systems configured substantially in accordance withthe use of the IS-95 standard are described in U.S. Pat. Nos. 5,103,459and 4,901,307, which are assigned to the assignee of the presentinvention and fully incorporated herein by reference. An exemplarydescribed system utilizing CDMA techniques is the cdma2000 ITU-R RadioTransmission Technology (RTT) Candidate Submission (referred to hereinas cdma2000), issued by the TIA. The standard for cdma2000 is given indraft versions of IS-2000 and has been approved by the TIA. The cdma2000proposal is compatible with IS-95 systems in many ways. Another CDMAstandard is the W-CDMA standard, as embodied in 3^(rd) GenerationPartnership Project “3GPP”, Document Nos. 3G TS 25.211, 3G TS 25.212, 3GTS 25.213, and 3G TS 25.214. Another CDMA standard is Interim StandardIS-856, which is commonly referred to as a High Data Rate (HDR) system.

Transmission of digital data is inherently prone to interference, whichmay introduce errors into the transmitted data. Error detection schemeshave been suggested to determine as reliably as possible whether errorshave been introduced into the transmitted data. For example, it iscommon to transmit data in packets and add to each packet a cyclicredundancy check (CRC) field, for example of a length of sixteen bits,which carries a checksum of the data of the packet. When a receiverreceives the data, the receiver calculates the same checksum on thereceived data and verifies whether the result of the calculation isidentical to the checksum in the CRC field.

When the transmitted data is not used in a delay sensitive application,it is possible to request retransmission of erroneous data when errorsare detected. However, when the transmission is used in a delaysensitive application, such as, e.g., in telephone lines, cellularphones, remote video systems, etc., it is not possible to requestretransmission.

Convolutional codes have been introduced to allow receivers of digitaldata to correctly determine the transmitted data even when errors mayhave occurred during transmission. The convolutional codes introduceredundancy into the transmitted data and pack the transmitted data intopackets in which the value of each bit is dependent on earlier bits inthe sequence. Thus, when errors occur, the receiver can still deduce theoriginal data by tracing back possible sequences in the received data.

To further improve the performance of a transmission channel,interleavers are used to re-order bits in the packet during coding.Thus, when interference destroys some adjacent bits during transmission,the effect of the interference is spread out over the entire originalpacket and can more readily be overcome by the decoding process. Otherimprovements may include multiple-component codes that encode the packetmore than once, in parallel or in series, or a combination thereof. Forexample, it is known in the art to employ an error correction methodthat uses at least two convolutional coders in parallel. Such parallelencoding is commonly referred to as turbo coding.

For multiple-component codes, optimal decoding is often a very complextask, and may require large periods of time not usually available foron-line decoding. Iterative decoding techniques have been developed toovercome this problem. Rather than determining immediately whetherreceived bits are zero or one, the receiver assigns each bit a value ona multilevel scale representative of the probability that the bit isone. Data represented on the multilevel scale is referred to as “softdata,” and iterative decoding is usually soft-in/soft-out, i.e., thedecoding process receives a sequence of inputs corresponding toprobabilities for the bit values and provides as output correctedprobabilities, taking into account constraints of the code. Generally, adecoder that performs iterative decoding uses soft data from formeriterations to decode the soft data read by the receiver. Duringiterative decoding of multiple-component codes, the decoder uses resultsfrom the decoding of one code to improve the decoding of the secondcode. When parallel encoders are used, as in turbo coding, twocorresponding decoders may conveniently be used in parallel for thispurpose. Such iterative decoding is carried out for a plurality ofiterations until it is believed that the soft data closely representsthe transmitted data. Those bits that have a probability indicating thatthey are closer to one are assigned binary zero, and the remaining bitsare assigned binary one.

Turbo coding represents an important advancement in the area of forwarderror correction (FEC). There are many variants of turbo coding, butmost types of turbo coding use multiple encoding steps separated byinterleaving steps combined with the use of iterative decoding. Thiscombination provides previously unavailable performance with respect tonoise tolerance in a communications system. Namely, turbo coding allowscommunications at levels of energy-per-bit per noise power spectraldensity (E_(b)/N₀) that were previously unacceptable using the existingforward error correction techniques.

Many communication systems use forward error correction techniques andtherefore would benefit from the use of turbo coding. For example, turbocodes could improve the performance of wireless satellite links, inwhich the limited downlink transmit power of the satellite necessitatesreceiver systems that can operate at low E_(b)/N₀ levels.

Digital wireless telecommunication systems also use forward errorcorrection. For example, the Telecommunications Industry Association haspromulgated the over-the-air interface standard TIA/EIA Interim Standard95, and its derivatives, such as, e.g., IS-95B (hereinafter referred tocollectively as IS-95), which define a digital wireless communicationssystem that uses convolutional encoding to provide coding gain toincrease the capacity of the system. A system and method for processingradio-frequency (RF) signals substantially in accordance with the use ofthe IS-95 standard is described in U.S. Pat. No. 5,103,459, which isassigned to the assignee of the present invention and fully incorporatedherein by reference.

It is an object of the embodiments described herein to provide enhanceddata throughput in systems utilizing turbo encoding.

SUMMARY

A novel and improved method and apparatus for enhancing data throughputof a wireless communication system are presented herein. In one aspect,an apparatus for increasing data throughput of a wireless communicationsystem is presented. The apparatus comprises a scheduler unit configuredto schedule a multi-slot packet transmission to a remote station inaccordance with a scheduling algorithm, wherein the scheduling algorithmuses a data request message from the remote station to determine aninitial set of transmission parameters and uses an acknowledgment signalfrom the remote station to determine a subsequent set of transmissionparameters; and a channel interleaver configured to perform apermutation of a plurality of data symbols separately from a permutationof a plurality of parity symbols, wherein the scheduler unit schedulesthe plurality of permuted data symbols for transmission at the beginningof the multi-slot packet transmission and schedules the plurality ofpermuted parity symbols at the end of the multi-slot packettransmission.

In another aspect, the apparatus further comprises a symbol generationelement for puncturing the output of the channel interleaver inaccordance with predetermined puncture patterns. Puncturing the outputhas the effect of truncating or shortening the output of the channelinterleaver.

In another aspect, a method for interleaving data and parity symbols fortransmission from a base station to a remote station in a wirelesscommunication system is presented. The method comprises the steps of:permuting a plurality of data symbols to form a first permutation block;permuting a plurality of parity symbols to form a second permutationblock; generating an output sequence by sequentially reading elements ofthe first permutation block and the second permutation block; andscheduling a multi-slot packet transmission from the base station to theremote station, wherein the scheduling packs data symbols of the outputsequence at the beginning of the multi-slot packet and parity symbols ofthe output sequence at the end of the multi-slot packet.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an exemplary voice and data communicationsystem.

FIG. 2 is a block diagram of a turbo encoder.

FIG. 3 is a block diagram of an apparatus that uses a turbo encoder togenerate forward traffic channels.

FIG. 4 is a flow chart of an embodiment that reorders the output of aturbo encoder.

FIG. 5 is a flow chart of another embodiment that reorders the output ofa turbo encoder.

FIG. 6 is a flow chart of another embodiment that reorders the output ofa turbo encoder.

FIG. 7A defines a one-to-one swap between bit groups for the 8-PSKmodulation scheme.

FIG. 7B defines a one-to-one swap between bit groups for the 16-QAMmodulation scheme.

FIG. 8 is a diagram of a signal constellation for the 8-PSK modulationscheme.

FIG. 9 is a diagram of a signal constellation for the 16-QAM modulationscheme.

DETAILED DESCRIPTION

As illustrated in FIG. 1, a wireless communication network 10 generallyincludes a plurality of mobile stations (also called subscriber units oruser equipment) 12A-12D, a plurality of base stations (also called basestation transceivers (BTSs) or Node B) 14A-14C, a base stationcontroller (BSC) (also called radio network controller or packet controlfunction 16), a mobile switching center (MSC) or switch 18, a packetdata serving node (PDSN) or internetworking function (IWF) 20, a publicswitched telephone network (PSTN) 22 (typically a telephone company),and an Internet Protocol (IP) network 24 (typically the Internet). Forpurposes of simplicity, four mobile stations 12A-12D, three basestations 14A-14C, one BSC 16, one MSC 18, and one PDSN 20 are shown. Itwould be understood by those skilled in the art that there could be anynumber of mobile stations 12, base stations 14, BSCs 16, MSCs 18, andPDSNs 20.

In one embodiment the wireless communication network 10 is a packet dataservices network. The mobile stations 12A-12D may be any of a number ofdifferent types of wireless communication device such as a portablephone, a cellular telephone that is connected to a laptop computerrunning IP-based, Web-browser applications, a cellular telephone withassociated hands-free car kits, a personal data assistant (PDA) runningIP-based, Web-browser applications, a wireless communication moduleincorporated into a portable computer, or a fixed location communicationmodule such as might be found in a wireless local loop or meter readingsystem. In the most general embodiment, mobile stations may be any typeof communication unit.

The mobile stations 12A-12D may be configured to perform one or morewireless packet data protocols such as described in, for example, theEIA/TIA/IS-707 standard. In a particular embodiment, the mobile stations12A-12D generate IP packets destined for the IP network 24 andencapsulate the IP packets into frames using a point-to-point protocol(PPP).

In one embodiment the IP network 24 is coupled to the PDSN 20, the PDSN20 is coupled to the MSC 18, the MSC 18 is coupled to the BSC 16 and thePSTN 22, and the BSC 16 is coupled to the base stations 14A-14C viawirelines configured for transmission of voice and/or data packets inaccordance with any of several known protocols including, e.g., E1, T1,Asynchronous Transfer Mode (ATM), IP, Frame Relay, HDSL, ADSL, or xDSL.In an alternate embodiment, the BSC 16 is coupled directly to the PDSN20, and the MSC 18 is not coupled to the PDSN 20. In another embodimentof the invention, the mobile stations 12A-12D communicate with the basestations 14A-14C over an RF interface defined in the 3^(rd) GenerationPartnership Project 2 “3GPP2,” “Physical Layer Standard for cdma2000Spread Spectrum Systems,” 3GPP2 Document No. C.P0002-A, TIA PN-4694, tobe published as TIA/EIA/IS-2000-2-A, (Draft, edit version 30) (Nov. 19,1999), which is fully incorporated herein by reference.

During typical operation of the wireless communication network 10, thebase stations 14A-14C receive and demodulate sets of reverse-linksignals from various mobile stations 12A-12D engaged in telephone calls,Web browsing, or other data communications. Each reverse-link signalreceived by a given base station 14A-14C is processed within that basestation 14A-14C. Each base station 14A-14C may communicate with aplurality of mobile stations 12A-12D by modulating and transmitting setsof forward-link signals to the mobile stations 12A-12D. For example, asshown in FIG. 1, the base station 14 a communicates with first andsecond mobile stations 12A, 12B simultaneously, and the base station 14Ccommunicates with third and fourth mobile stations 12C, 12Dsimultaneously. The resulting packets are forwarded to the BSC 16, whichprovides call resource allocation and mobility management functionalityincluding the orchestration of soft handoffs of a call for a particularmobile station 12A-12D from one base station 14A-14C to another basestation 14A-14C. For example, a mobile station 12C is communicating withtwo base stations 14B, 14C simultaneously. Eventually, when the mobilestation 12C moves far enough away from one of the base stations 14C, thecall will be handed off to the other base station 14B.

If the transmission is a conventional telephone call, the BSC 16 willroute the received data to the MSC 18, which provides additional routingservices for interface with the PSTN 22. If the transmission is apacket-based transmission such as a data call destined for the IPnetwork 24, the MSC 18 will route the data packets to the PDSN 20, whichwill send the packets to the IP network 24. Alternatively, the BSC 16will route the packets directly to the PDSN 20, which sends the packetsto the IP network 24.

In some exemplary CDMA systems, packets carrying data traffic aredivided into subpackets, which occupy “slots” of a transmission channel.For illustrative ease only, the nomenclature of a High Data Rate (HDR)system is used herein. Such use is not intended to limit theimplementation of the invention to HDR systems. Embodiments can beimplemented in other CDMA systems, such as, e.g. cdma2000, withoutaffecting the scope of the embodiments described herein.

In an HDR system, slot sizes have been designated as 1.66 ms, but itshould be understood that slot sizes might vary in the embodimentsdescribed herein without affecting the scope of the embodiments. Forexample, the slot size in cdma2000 systems is 1.25 ms in duration. Inaddition, data traffic can be transmitted in message frames, which canbe 5 ms, 10 ms, 20 ms, 40 ms or 80 ms in duration in IS-95 systems. Theterms “slots” and “frames” are terms used with respect to different datachannels within the same or between different CDMA systems. A CDMAsystem comprises a multitude of channels on the forward and reverselinks, wherein some channels are structured differently from others.Hence, the terminology to describe some channels will differ inaccordance with channel structure. For illustrative purposes only, theterm “slots” will be used hereafter to describe the packaging of signalspropagated over the air.

Redundant representations of the data payload are packed into frames, orsubpackets, which can then be soft-combined at the receiver. Redundancyrefers to the substantially similar information carried by eachsubpacket. Redundant representations may be generated either throughrepetition or through additional coding. The process of soft-combiningallows the recovery of corrupted bits. Through the process of softcombining, wherein one corrupted subpacket is combined with anothercorrupted subpacket, the transmission of repetitious and redundantsubpackets can allow a system to transmit data at a minimum transmissionrate. The transmission of repetitious and redundant subpackets isespecially desirable in the presence of fading. Rayleigh fading, whichis a form of multipath interference, occurs when multiple copies of thesame signal arrive at the receiver at different phases, potentiallycausing destructive interference. Substantial multipath interferencewith very small delay spread can occur to produce flat fading over theentire signal bandwidth. If the remote station is traveling in a rapidlychanging environment, deep fades could occur at times when subpacketsare scheduled for retransmission. When such a circumstance occurs, thebase station requires additional transmission power to transmit thesubpacket.

For example, if a scheduler unit within a base station receives a datapacket for transmission to a remote station, the data payload isredundantly packed into a plurality of subpackets, which aresequentially transmitted to a remote station. When transmitting thesubpackets, the scheduler unit may decide to transmit the subpacketseither periodically or in a channel sensitive manner.

The forward link from the base station to a remote station operatingwithin the range of the base station can comprise a plurality ofchannels. Some of the channels of the forward link can include, but arenot limited to a pilot channel, synchronization channel, paging channel,quick paging channel, broadcast channel, power control channel,assignment channel, control channel, dedicated control channel, mediumaccess control (MAC) channel, fundamental channel, supplemental channel,supplemental code channel, and packet data channel. The reverse linkfrom a remote station to a base station also comprises a plurality ofchannels. Each channel carries different types of information to thetarget destination. Typically, voice traffic is carried on fundamentalchannels, and data traffic is carried on supplemental channels or packetdata channels. Supplemental channels are usually dedicated channels,while packet data channels usually carry signals that are designated fordifferent parties in a time-multiplexed manner. Alternatively, packetdata channels are also described as shared supplemental channels. Forthe purposes of describing the embodiments herein, the supplementalchannels and the packet data channels are generically referred to asdata traffic channels.

Supplemental channels and packet data channels can improve the averagetransmission rate of the system by allowing the transmission ofunexpected data messages to a target station. Since the data payload canbe redundantly packed on these channels, a multi-slot transmissionscheduled on the forward link can be terminated early if the remotestation can determine that the data payload is recoverable from thesubpackets that have already been received. As described above, the datapayload that is carried in each slot has undergone various encodingsteps wherein the encoded bits are re-ordered into a channel-tolerantformat. Hence, in order to accomplish data recovery, the decoder of theremote station must operate on the entire contents of each slot of themulti-slot transmission. However, operation of the decoder after eachslot is a power-intensive process that can inordinately drain thebattery power of the remote station.

The embodiments described herein will reduce the power drain due to theoperation of the decoder by allowing the decoder to operate on partialtransmissions of data packets. In addition to reducing the power drain,the embodiments allow a minimum transmission rate to be maintained.

Determining Data Transmission Rates on the Forward Link

In an HDR system, the rates at which the subpackets are to betransmitted from a base station to a remote station are determined by arate control algorithm performed by the remote station and a schedulingalgorithm at the base station. This method to modify the datatransmission rate is referred to as an Automatic Repeat Request (ARQ)procedure. It should be noted that the system throughput is determinedby the rate at which data payload is actually received, which differsfrom the bit rate of the transmitted subpackets.

The rate control algorithm is implemented by the remote station in orderto determine which base station in the active set can provide the bestthroughput and to determine the maximum data rate at which the remotestation can receive packets with sufficient reliability. The active setis the set of base stations that are currently in communication with theremote station. In a typical CDMA or non-CDMA wireless system, a basestation transmits a known signal, referred to as a “pilot,” atwell-defined, periodic intervals. The remote station typically monitorsthe pilot signal of each base station maintained in the active set, anddetermines the signal-to-noise-and-interference ratio (SINR) of eachpilot signal. Based on past SINR information, the remote stationpredicts a future value of the SINR for each base station, wherein thefuture value of the SINR will be associated with the next packetduration. The remote station then picks the base station that is likelyto have the most favorable SINR over a period of the near future, andestimates the best data rate at which the remote station can receive thenext data packet from this base station. The remote station thentransmits a data rate control message (DRC) carrying this data rateinformation to the base station. It is understood that the best datarate information carried by the DRC is the data rate at which the remotestation requests the next data packet to be transmitted. In an HDRsystem, the DRC messages are transmitted on a MAC channel of the reverselink waveform.

The scheduling algorithm is implemented at the base station to determinewhich remote station will be the recipient of the next packet. Thescheduling algorithm takes into account the need to maximize basestation throughput, the need to maintain fairness between all remotestations operating within the range of the base station, and the need toaccommodate the data transmission rates requested by various remotestations. As discussed below, the fast ARQ procedure determines theactual data transmission rate at which each data packet is received, asopposed to the data transmission rate initially determined by the ratecontrol algorithm.

A scheduling unit in the base station monitors the arrival of DRCs fromall remote stations that are operating within its range, and uses theDRC information in the scheduling algorithm to determine which remotestation will be the next data packet recipient, in accordance with anoptimal forward link throughput level. It should be noted that anoptimal forward link throughput takes into consideration the maintenanceof acceptable link performances for all remote stations operating withinthe range of the base station. The scheduling unit reassembles the datapacket into subpackets with the appropriate bit rate, and generates atransmission schedule for the subpackets on designated slots.

In an HDR system, the forward link data rates vary from 38.4 kbps to2.456 Mbps. The duration of each packet transmission in number of slotsas well as other modulation parameters are described in Table 1.

TABLE 1 Forward Link Modulation Parameters Data Rate Number Bits perCode (kbps) of Slots Packet Rate Modulation 38.4 16 1024 1/5 QPSK 76.8 81024 1/5 QPSK 153.6 4 1024 1/5 QPSK 307.2 2 1024 1/5 QPSK 614.4 1 10241/3 QPSK 307.2 4 2048 1/3 QPSK 614.4 2 2048 1/3 QPSK 1228.8 1 2048 2/3QPSK 921.6 2 3072 1/3 8-PSK 1843.2 1 3072 2/3 8-PSK 1228.8 2 4096 1/316-QAM 2457.6 1 4096 2/3 16-QAM

In an HDR system, code symbols that are transmitted in subpackets atlower data rates are code-extensions or repetitions of the code symbolsthat are transmitted at certain higher rates. In many cases, the codesymbols transmitted in a given subpacket are shifted repetitions of thecode symbols transmitted in the earlier slots of the packet. The lowerdata rates require a lower SINR for a given low probability of packeterror. Hence, if the remote station determines that channel conditionsare not favorable, the remote station will transmit a DRC messagerequesting a low data rate packet, which comprises multiple subpackets.The base station will then transmit multi-slot packets in accordancewith parameters stored in the scheduling unit, an example of which ispresented in Table 1.

As the subpackets are transmitted, the remote station may determine thatthe data packet can be decoded from only a portion of the subpacketsscheduled for transmission. Using the fast ARQ procedure, the remotestation instructs the base station to stop the transmission of theremaining subpackets, thereby increasing the effective data transmissionrate of the system. However, in order to cause the early termination ofthe scheduled subpacket transmissions, the remote station may have torun the decoder over every slot carrying a subpacket, which requires theconsumption of a large amount of power.

It should be noted that the ARQ procedure has the potential tosignificantly increase the forward link throughput of the underlyingwireless communication system. As discussed above, when the remotestation transmits a DRC message to the base station, the requested datatransmission rate is determined using the rate control algorithm, whichuses past SINR values to predict the SINR value of the near future.However, due to fading conditions that arises due to environmentalfactors and the mobility of the remote station, the prediction of theSINR for the near future is not reliable. In addition, the SINR of theforward link traffic signal may be very different from the SINR of thepilot signal due to interference from adjacent base stations. It ispossible that some of the neighboring base stations may have been idleduring the sampling period for the SINR prediction calculations. As aresult, the remote station may not always predict the SINR with greataccuracy. Therefore, the rate control algorithm provides a lower boundestimate for the actual SINR during the next packet duration with highprobability, and determines the maximum data transmission rate that canbe sustained if the actual SINR is equal to this lower bound estimate.In other words, the rate control algorithm provides a conservativemeasure of the data transmission rate at which the next packet can bereceived. The ARQ procedure refines this estimate, based on the qualityof the data received during the initial stages of the packettransmission. Hence, it is important for the remote station to informthe base station as soon as the remote station has enough information todecode a data packet, so that early termination of transmissions canoccur, which enhances the data transmission rate of the data packet.

Transmissions of the subpackets to the remote station are sent in astaggered pattern so that transmission gaps occur between thesubpackets. In one embodiment, the subpackets are transmittedperiodically at every 4^(th) slot. The delay between subpackets providesan opportunity for the target remote station to decode the subpacketbefore the arrival of the next subpacket. If the remote station is ableto decode the subpacket before the arrival of the next subpacket and toverify the Cyclic Redundancy Check (CRC) bits of the decoded resultbefore the arrival of the next subpacket, the remote station cantransmit an acknowledgment signal, hereinafter referred to as a FAST_ACK(acknowledgement) signal, to the base station. If the base station candemodulate and interpret the FAST_ACK signal sufficiently in advance ofthe next scheduled subpacket transmission, the base station need notsend the remaining scheduled subpacket transmissions. The base stationmay then transmit a new data packet to the same remote station or toanother remote station during the slot period that had been designatedfor the cancelled subpackets. It should be noted that the FAST_ACKsignal herein described is separate and distinct from the ACK messagesthat are exchanged between the higher layer protocols, such as the RadioLink Protocol (RLP) and the Transmission Control Protocol (TCP).

Since the ARQ procedure allows a fast rate adaptation to channelconditions, the ARQ procedure allows for the implementation of a systemwherein the initial data transmission can be performed at a high datarate and ramped down as needed. In contrast, a system without ARQ wouldbe forced to operate at a lower data rate, in order to provide asufficient link budget margin to account for channel variations duringpacket transmissions.

Reducing Power Consumption by Reducing Decoder Operation

In one embodiment, the remote station can reduce the power consumptionof the decoder by operating the decoder in accordance with statisticalproperties of the channel. The remote station determines the averageSINR of the pilot signal corresponding to the arrival times of receivedsubpackets. It should be noted that the average traffic channel SINR maybe higher than the average SINR of the pilot channel, due to theinactivity of neighboring base stations during the packet transmission,and that the average pilot channel SINR is subject to measurement noise,which also introduces uncertainty in the average traffic channel SINR.The remote station compares the average SINR to an entry in a lookuptable. For each data rate, the lookup table associates a number ofsubpackets (i.e., transmission slots) to a required packet SINR level,the required packet SINR level being a threshold value for which packetinformation can be obtained at a low error rate from a minimum number ofsubpackets. The entries in this lookup table may be base on simulationor controlled testing of the remote station demodulator performanceunder various channel conditions.

If the average SINR is considerably lower than the correspondingrequired packet SINR level in the look-up table, then the remote stationrefrains from decoding the received subpackets and waits for the nextsubpacket arrival. The remote station continues the process of makingaverage SINR calculations of the pilot signals.

If the average SINR is lower than the corresponding required packet SINRlevel in the look-up table, but remains within a tolerance value, and ifthe actual SINR over the data period is significantly higher than theaverage pilot channel SINR, then the remote station may decode thereceived subpackets. The remote station operates the decoder for a smallnumber of iterations. If the decoding is successful, then the remotestation transmits a FAST_ACK signal to the base station.

If the average SINR is larger than the required packet SINR level in thelook-up table by a second tolerance value, then the remote stationoperates the decoder for a small number of iterations. It should beobserved that if the traffic channel has a favorable SINR level, thenthe transmitted subpackets could likely be decoded with a small numberof iterations.

If the average SINR is in the close vicinity of the required packet SINRlevel in the look-up table, then the remote station operates the decoderfor a large number of iterations. In an embodiment described below, adynamic stopping criterion is presented to limit the number ofiterations of the decoder.

In the embodiment described above, positive, real-valued parametersΔ₁≥Δ₂≥0, and Δ₃≥0 can be set, and non-negative integer-valued parameters0≤N₁≤N₂≥N, ≥0 can be set. Let S denote the average SINR measured overthe first few received subpackets, and let T denote the required packetSINR threshold from the look-up table, for the given (initial) datarate, over the given number of subpackets. If S<T−Δ₁, then the mobiledoes not attempt to decode the packet with currently available data. IfT−Δ₁≤S<T−Δ₂, then the mobile attempts to decode the packet with amaximum of N₁ iterations. If T−Δ₂≤S<T+Δ₃, then the mobile attempts todecode the packet with a maximum of N₂ iterations. If S≥T+Δ₃, then themobile attempts to decode the packet with a maximum of N₃ iterations. Inall cases, a dynamic stopping rule is implemented, which prevents thedecoder from running too many iterations after the packet has beensuccessfully decoded.

Turbo decoding is an iterative procedure, wherein a symbol is decodedafter a specified number of iterations. A dynamic stopping rule can bedesigned to avoid running iterations after the symbol is successfullydecoded, while retaining the ability to use a large number of decodingiterations only for badly degraded code symbols.

In one embodiment, a dynamic stopping rule is implemented to producesignificant power savings while maintaining a high data transmissionrate. A minimum number of iterations N_(min) and a maximum number ofiterations N_(max) are set at the remote station. N_(min) iterations arerun. The CRC bits of the decoded payload are determined and compared tothe CRC bits of the decoded packet. If the two sets of CRC bits areequal, then the CRC bits are deemed valid and the decoder is run for asuccessive iteration to determine if a subsequent payload has valid CRCbits. If the two sets of CRC bits are not equal, then the CRC bits aredeemed invalid and another iteration is run. If the CRC bits from twosuccessive iterations are both deemed valid, then the decoding is deemedsuccessful and terminated. If the number of iterations reaches N_(max),the decoding is terminated.

Transmitting Interleaved Symbols that Minimize Decoder Operations

In another embodiment to reduce decoder operations, which can be used inconjunction with the dynamic stopping rule and the channel sensitivemethod described above or can be implemented independently from thedynamic stopping rule and channel sensitive method described above, thesubpackets can be transmitted in a manner that allows the decoder todetermine the payload of the partial slot transmissions quickly, whilestill providing protection from burst errors.

A channel interleaver can be configured in accordance with thisembodiment to permute the bits of an encoded symbol and provideincremental redundancy. In this embodiment, a permutation of the bits isdesigned so that the systematic bits are sent during a partialtransmission of the multi-slot packet. The decoder may be able todetermine the data payload from the arrival of only a portion of thesubpackets. If the payload cannot be decoded, then the remote stationtransmits a negative acknowledgment (NAK) on the ARQ channel. The basestation receives the NAK and transmits a subsequent subpacket,containing additional parity bits. If the remote station cannot decodethe subpackets with the already received systematic bits and the newlyreceived parity bits, then another NAK is transmitted. The base stationreceives the second NAK and transmits another subpacket, which includesadditional parity bits. As further NAKs are received during the ARQprocedure, subsequent subpackets transmitted by the base station containmore parity bits.

In other words, the channel interleaver permutes the systematic bits andthe parity bits in a manner such that the systematic bits are loaded atthe front of a packet and the parity bits are loaded at the rear of thepacket. For transmission purposes, the packet is divided up intoportions, and each portion is transmitted sequentially, as needed by theremote station. Hence, if additional information is needed to decode thedata payload, only the additional parity bits are transmitted, ratherthan retransmitting the entire encoder output.

This process of loading systematic bits at the beginning of thescheduled packet transmission may appear to defeat the purpose of achannel interleaver, but the embodiment described herein can beimplemented to provide resilience to burst errors while still allowingthe decoder to operate on only a partial transmission of the packet. Inmost implementations of power-efficient, wireless communication systemsusing turbo codes, the output of the turbo encoder is scrambled eitherbefore or after channel interleaving so that data is randomized prior tomodulation. The random scrambling of the turbo encoder output limits thepeak-to-average ratio of the envelope of the modulated waveform.

FIG. 2 is a block diagram of a turbo encoder that is configured tooperate with the channel interleaver embodiments herein described. Turboencoder 200 comprises a first constituent encoder 210, a turbointerleaver 220, a second constituent encoder 230, and a symbolgeneration element 240. The first constituent encoder 210 and the secondconstituent encoder 230 are connected in parallel, with the turbointerleaver 220 preceding the second constituent encoder 230. The outputof the first constituent encoder 210 and the output of the secondconstituent encoder 230 are input into the symbol generation element240, wherein the outputs are punctured and repeated in order to form thedesired number of turbo encoder output symbols.

In one embodiment, the first and second constituent encoders 210, 230are recursive, convolutional encoders, each configured in accordancewith the transfer function:G(D)=[1,n ₀(D)/d(D),n ₁(D)/d(D)],wherein d(D)=1+D²+D³, n₀(D)=1+D+D³, and n₁(D)=1+D+D²+D³. Using the firstand second constituent encoders 210, 230, the turbo encoder 200generates a plurality of encoded data output symbols and a plurality ofencoded tail output symbols, wherein the plurality of encoded dataoutput symbols are subsequently punctured by the symbol generationelement 240 and the plurality of encoded tail output symbols aresubsequently both punctured and repeated by the symbol generationelement 240.

Initially, the states of the first constituent encoder 210 and thesecond constituent encoder 230 are set to zero. Let N_(turbo) be thenumber of data bits input into the turbo encoder 200, after a 6-bitPhysical Layer packet tail field is discarded. The first constituentencoder 210 is clocked once for each of the N_(turbo) bits with theswitch 250 in the up position. The second constituent encoder 230 isalso clocked once for each of the N_(turbo) bits with the switch 250 inthe up position. The resultant encoded data symbols are inputsequentially into symbol generation element 240, in the order X, Y₀, Y₁,X′, Y′₀, and Y′₁, with the X output first. The sequence X, Y₀, Y₁, X′,Y′₀, Y′₁ is then punctured by the symbol generation element 240, in themanner specified below in Table 2.

TABLE 2 Puncturing Patterns for Encoded Data Symbols. Output Code Rate1/3 Code Rate 1/5 X 1 1 Y₀ 1 1 Y₁ 0 1 X′ 0 0 Y′₀ 1 1 Y′₁ 0 1 (For eachrate, the puncturing table is read from top to bottom.)

In Table 2, “0” indicates that the symbol will be deleted, and “1”indicates that the symbol will be passed. In this embodiment, symbolrepetition is not used in generating the encoded data output symbols.

After the packet data bits have been encoded into data symbols, theturbo encoder 200 generates tail output symbols. The tail output symbolsare generated by clocking each of the constituent encoders for half ofthe duration of the total tail bit periods while the other constituentencoder is left unclocked. For example, in the embodiment wherein therate of the turbo encoder is R, and the number of tail output symbolsdesired is 6/R, then the first 3/R tail output symbols are generatedwhen the first constituent encoder 210 is clocked three times with theswitch 250 in the down position and the second constituent encoder 230is not clocked. Hence, no output is generated by the constituent encoder230 during this period. The resultant encoded tail output symbolsundergo puncturing and symbol repetition at symbol generation element240. The last 3/R tail output symbols are generated when the secondconstituent encoder 230 is clocked three times with the switch 250 inthe down position while the first constituent encoder 210 is notclocked. The resultant encoded tail output symbols undergo puncturingand symbol repetition at symbol generation element 240.

The outputs of the first and second constituent encoders 210, 230 areinput into symbol generation element 240 in the sequence X, Y₀, Y₁, X′,Y′₀, and Y′₁, with the X output first. Sequence X, Y₀, Y₁, X′, Y′₀, andY′₁ of the encoded tail output symbols are punctured in accordance withTable 3 below. In Table 3, “0” indicates that the symbol will deleted,and “1” indicates that the symbol passes.

TABLE 3 Puncturing Patterns for Tail Bit Periods. Output Code Rate 1/3Code Rate 1/5 X 111 000 111 000 Y₀ 111 000 111 000 Y₁ 000 000 111 000 X′000 111 000 111 Y′₀ 000 111 000 111 Y′₁ 000 000 000 111(For rate R=1/3 turbo codes, the puncturing table is read first from topto bottom, repeating X and X′, and then from left to right. For rateR=1/5 turbo codes, the puncturing table is read first from top tobottom, repeating X, X′, Y₁ and Y′₁, and then from left to right.)

For rate R=1/5, the tail output code symbols for each of the first threetail bit periods can be punctured and repeated to form the sequenceXXY₀Y₁Y₁. The tail output code symbols for each of the last three tailbit periods are punctured and repeated to form the sequenceX′X′Y′₀Y′₁Y′₁. For rate R=1/3, the tail output code symbols of the firstthree tail bit periods are punctured and repeated to form the sequenceXXY₀. The tail output code symbols of the last three tail bit periodsare punctured and repeated to form the sequence X′X′Y′₀.

FIG. 3 is a block diagram of an apparatus that uses a turbo encoder togenerate forward traffic channels. Data packets are input into a turboencoder 300. Turbo encoder 300 can be configured in the manner describedfor FIG. 2, but alternative configurations can be implemented withoutaffecting the scope of the embodiments. In one embodiment, a scrambler310 is used to randomize the output of the turbo encoder 300. Scrambler310 can be implemented by a linear feedback shift register (LSFR), whichis configured in accordance with the generator sequence h(D)=D¹⁷+D¹⁴+1.Every output code symbol of the turbo encoder 300 is XORed with anoutput bit of the scrambler 310. The scrambler 310 can be initialized byinformation such as the MAC index value and/or the data rate, and isclocked once for every encoder output symbol. The output of thescrambler 310 is interleaved by a channel interleaving element 320. Theinterleaving is implemented in accordance with the embodiments describedbelow.

Various implementations of a channel interleaving element 320 can beused to realize the embodiments described below. For example, a channelinterleaving element can be produced using at least one memory elementand a processor. Alternatively, a lookup table of READ addresses orWRITE addresses may be used permute an array of input symbols togenerate an array of interleaved symbols. In another alternative, astate machine can be used to generate a sequence of addresses definingthe permutation of input symbols. Other implementations are known tothose of skill in the art, and will not be described herein. The choiceof implementation will not affect the scope of the embodiments below.

The output of the channel interleaving element 320 is separated intoin-phase (I) and quadrature phase (Q) sequences by modulation element330. Modulation element 330 is configured to perform Quadrature PhaseShift Keying (QPSK), 8-ary Phase Shift Keying (PSK), and 16-aryQuadrature Shift Keying (QSK) modulation upon the interleaved symbols,wherein the choice of modulation scheme is determined based on the datatransmission rate of the packet. An example of the choice of themodulation schemes based on data transmission rates is presented inTable 1. The output of the modulation element 330 undergoes furtherprocessing, in accordance with the type of CDMA system in which theembodiments are implemented. The additional processing steps will not bedescribed herein since these processing steps are not directly relevantto the understanding of the scope of the embodiments. Descriptions ofthe specific processing steps can be found in the aforementioned CDMAdocuments.

In one embodiment, the output of a turbo encoder operating at rate 1/5can be reordered by the method described in FIG. 4, wherein all the dataand tail output symbols are demultiplexed into five sequences, denotedU, V₀, V₁, V′₀ and V′₁. At step 400, the output symbols are sequentiallydistributed from the U sequence to the V′₁ sequence, wherein the firstoutput symbol is placed in the U sequence, the second output symbol isplaced in the V₀ sequence, the third output symbol is placed in the V₁sequence, the fourth output symbol is placed in the V′₀ sequence, andthe fifth output symbol is placed in the V′₁ sequence. The next,subsequent output symbols repeat this pattern. At step 402, the U, V₀,V₁, V′₀ and V′₁ sequences are rearranged according to the order U, V₀,V′₀, V₁, and V′₁. It should be noted that this order can altered as longas the U sequence remains first, and the V₁ and V′₁ sequences are placedat the end of the order.

In an embodiment wherein the turbo encoder is operating at rate 1/3, thedemultiplexing can be completed using three sequences, denoted U, V₀,and V′₀. In this case, the rearrangement of the order of V₀, and V′₀results in an equivalent interleaver from the viewpoint of errorperformance, since the requirement that the first and last sequencesremain at the first position and last position has not been violated.

In the embodiment wherein the turbo encoder operates at rate=1/5, thechannel interleaver will be configured to permute code symbols in threeseparate bit-reversal interleaver blocks with the first block comprisingthe sequence of U symbols, the second block comprising the sequence ofV₀ and V′₀ symbols, and the third block comprising the sequence of V₁and V′₁ symbols. In the embodiment wherein the turbo encoder operates atrate=1/3, the channel interleaver will be configured to permute codesymbols in two separate blocks, with the first block comprising thesequence of U sequences and the second block comprising the sequence ofV₀ and V′₀ symbols. For the sake of illustrative ease, the embodimentfor rate R=1/3 will not be described hereinafter because the embodimentfor rate R=1/3 operates in the same manner as the embodiment for rateR=1/5, which is described in detail below in FIG. 5.

In the embodiment wherein a scrambling element is used upon the outputsymbols of the turbo encoder before channel interleaving occurs, theabove embodiment can still be implemented upon a block of scrambled Usymbols, a block of scrambled V₀ and V′₀ symbols, and a block of thescrambled V₁ and V′₁ symbols.

FIG. 5 is a flow chart for a series of permutation steps in accordancewith one embodiment. At step 500, sequences U, V₀, V′₀, V₁, and V′₁ arewritten into rectangular arrays of K rows and M columns to form a firstinput block U, a second block V₀/V′₀, and a third input block V₁/V′₁.The symbols are written into the blocks by rows, wherein symbols areplaced starting from the top row and are placed from left to right. Thecolumns of the blocks are labeled by the index j, where j=0, . . . , M−1and column 0 is the left-most column.

At step 502, the symbols of each column of input block U are end-aroundshifted downward by j mod(K), the symbols of each column of input blockV₀/V′₀ are end-around shifted downward by └j/4┘ mod (K), and the symbolsof each column of input block V₁/V′₁ are also end-around shifteddownward by └j/4┘ mod (K). The floor operator └ ┘ is used to denote thehighest integer value less than or equal to the value within the flooroperator.

At step 504, the columns are reordered so that column j is moved tocolumn BRO(j), wherein BRO(j) indicates the bit-reversed value of j. Forexample, for M=512, BRO(6)=192.

At step 506, the entire array of symbols is read out column-wise,starting from the left-most column, and read from top to bottom.

Using this method, the interleaver output sequence for a turbo encoderat rate=1/5 will be the interleaved U symbols followed by theinterleaved V₀/V′₀ symbols and then the interleaved V₁/V′₁ symbols. Atrate=1/3, the interleaver output sequence will be the interleaved Usymbols followed by the interleaved V₀/V′₀ symbols. Various values forparameters K and M are presented in Table 2.

TABLE 2 Channel Interleaver Parameters U Block V₀/V′₀ and V₁/V′₁ BlockPhysical Layer Interleaver Parameters Interleaver Parameters Packet SizeK M K M 1,024 2 512 2 1,024 2,048 2 1,024 2 2,048 3,072 3 1,024 3 2,0484,096 4 1,024 4 2,048

Higher rate codes may be generated simply by discarding or truncatingthe last few outputs of the interleaver. This procedure provides resultsthat approximate optimal or near optimal turbo codes operating at rate4/5, 2/3, 1/2, 1/3, 1/4, and 1/5, with the appropriate puncturepatterns, as shown in Table 3.

TABLE 3 Puncture Patterns for the three Rate 2/3 codes Symbol Order X Y₀Y₀′ Y₁ Y₁′ X Y₀ Y₀′ Y₁ Y₁′ X Y₀ Y₀′ Y₁ Y₁′ X Y₀ Y₀′ Y₁ Y₁′ Rate 4/5 1 11 0 0 1 0 0 0 0 1 0 0 0 0 1 0 0 0 0 Rate 4/5 1 0 0 0 0 1 0 0 0 0 1 0 0 00 1 0 0 0 0 (cont'd) Rate 2/3 1 1 1 0 0 1 0 0 0 0 1 0 0 0 0 1 0 0 0 0Rate 1/2 1 1 1 0 0 1 0 0 0 0 1 1 1 0 0 1 0 0 0 0 Rate 1/3 1 1 1 0 0 1 11 0 0 1 1 1 0 0 1 1 1 0 0 Rate 1/5 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 11

In another embodiment, the channel interleaver can be configured toincrease performance for higher order modulation schemes. As shown inTable 1, an HDR system can accommodate variable transmission rates ofdata by utilizing different modulation schemes. In one embodiment, aninterleaving pattern is designed to enhance the performance of 8-aryPhase Shift Keying (PSK) modulation and 16-ary Quadrature AmplitudeModulation (QAM).

FIG. 6 is a flow chart for a series of permutation steps in accordancewith one embodiment. At step 600, sequences U, V₀, V′₀, V₁, and V′₁ arewritten into rectangular arrays of K rows and M columns to form a firstinput block U, a second block V₀/V′₀, and a third input block V₁/V′₁.The symbols are written into the blocks by rows, wherein symbols arewritten starting from the top row and are written from left to right.The columns of the blocks are labeled by the index j, where j=0, . . . ,M−1 and column 0 is the left-most column.

At step 602, the columns are reordered so that column j is moved tocolumn BRO(j), wherein BRO(j) indicates the bit-reversed value of j. Forexample, for M=512, BRO(6)=192.

At step 604, a block swap takes place in accordance with the type ofmodulation scheme that is to follow the channel interleaver. In anembodiment wherein the 8-PSK modulation scheme will be used in an HDRsystem, FIGS. 7A and 7B are tables that show the placement of certaingroups of bits that can be exchanged with other bits, wherein theone-to-one swap is identified by a number and an accent mark. Forexample, bits in Group 1 will be exchanged with bits in Group 1′. FIG.7A is an optimal swapping pattern for an 8-PSK modulation scheme andFIG. 7B is an optimal swapping pattern for a 16-QAM modulation scheme.The optimality of the swapping patterns herein disclosed is determinedthrough empirical observation.

At step 606, the entire array of symbols is read out by columns,starting from the left-most column, and read from top to bottom.

The results from this embodiment optimize the placement of turbo encoderoutput into the modulation symbols in the multi-slot packettransmission. This embodiment exploits properties of the 8-PSK and the16-QAM modulation schemes, namely, various bits of the modulationsymbols have different levels of protection and the various bits aredistributed uniformly in the modulation pattern.

In one embodiment, an 8-PSK modulation scheme is used to modulate thesignal. FIG. 8 illustrates a signal constellation for the 8-PSKmodulation. Three successive channel interleaver output symbols, x(3i),x(3i+1), and x(3i+2), i=0, . . . , M−1, are mapped to the signalconstellation point (m₁(i), m_(Q)(i)). Table 4 specifies the mapping ofthe interleaved symbols to the modulation symbols.

TABLE 4 8—PSK Modulation Interleaved Symbols s₂ s₁ s₀ Modulation Symbolsx(3 k + 2) x(3 k + 1) x(3 k) m_(I)(k) m_(Q)(k) 0 0 0   C   S 0 0 1   S  C 0 1 1 −S   C 0 1 0 −C   S 1 1 0 −C −S 1 1 1 −S −C 1 0 1   S −C 1 0 0  C −S (Note: C = cos(π/8) and S = sin(π/8) )

From the symbol mapping in FIG. 8, it can be observed that the mostsignificant bit s₂ is resilient to errors on the quadrature channel,i.e., a positive modulation symbol value would be interpreted as a “0”with a high degree of certainty whereas a negative modulation symbolvalue would be interpreted as a “1” with a high degree of certainty. Thesame would be true for the bit s₁ and the in-phase channel. However, thesame would not be true for the least significant bit s₀. The embodimentsdescribed above distributes the protected bits and the unprotected bitsuniformly along the packet.

In another embodiment, a 16-QAM is used to modulate the signal. FIG. 9illustrates a signal constellation for the 16-QAM modulation scheme.Four successive channel interleaver output symbols, x(4i), x(4i+1),x(4i+2), and x(4i+3), i=0, . . . , M−1, are mapped to the signalconstellation point (m₁(i), m_(Q)(i)). Table 5 specifies the mapping ofthe interleaved symbols to the modulation symbols.

TABLE 5 16-QAM Modulation, where A = 1/√10 Interleaved Symbols S₃ s₂ s₁s₀ Modulation Symbols x(4 k + 3) x(4 k + 2) x(4 k + 1) x(4 k) M_(Q)(k)M_(I)(k) 0 0 0 0 3A 3A 0 0 0 1 3A  A 0 0 1 1 3A −A 0 0 1 0 3A −3A  0 1 00  A 3A 0 1 0 1  A  A 0 1 1 1  A −A 0 1 1 0  A −3A  1 1 0 0 −A 3A 1 1 01 −A  A 1 1 1 1 −A −A 1 1 1 0 −A −3A  1 0 0 0 −3A  3A 1 0 0 1 −3A   A 10 1 1 −3A  −A 1 0 1 0 −3A  −3A 

If the number of required modulation symbols is more than the numberprovided in the above embodiments, then the complete sequence of inputmodulation symbols can be repeated as many full-sequence times aspossible followed by a partial transmission of a sequence. If a partialtransmission is needed, the first portion of the input modulation symbolsequence can be used. Similarly, if the number of required modulationsymbols is less than the number provided, only the first portion of theinput modulation symbol sequence can be used.

Table 6 provides an example of sequence repetition and puncturingparameters that can be used with the above embodiments. The number ofmodulation symbols that the modulator can provide per physical layerpacket and the number of modulation symbols needed for that data portionof the allocated slots are presented.

TABLE 6 Sequence Repetition and Symbol Puncturing Parameters # of # ofData # of # of Full Mod. Sym. Rate # of # of Mod. Sym. Mod. Sym.Sequence in Last Code Repeat (kbps) Slots Bits Provided Needed TxPartial Tx Rate Factor 38.4 16 1024 2560 24576 9 1536 1/5 9.6 7.8 8 10242560 12288 4 2048 1/5 4.8 153.6 4 1024 2560 6144 2 1024 1/5 2.4 307.2 21024 2560 3072 1 512 1/5 1.2 614.4 1 1024 1536 1536 1 0 1/3 1 307.2 42048 3072 6272 2 128 1/3 2.04 614.4 2 2048 3072 3136 1 64 1/3 1.021228.8 1 2048 3072 1536 0 1536 2/3 1 921.6 2 3072 3072 3136 1 64 1/31.02 1843.2 1 3072 3072 1536 0 1536 2/3 1 1228.8 2 4096 3072 3136 1 641/3 1.02 2457.6 1 4096 3072 1536 0 1536 2/3 1

Those of skill in the art would understand that information and signalsmay be represented using any of a variety of different technologies andtechniques. For example, data, instructions, commands, information,signals, bits, symbols, and chips that may be referenced throughout theabove description may be represented by voltages, currents,electromagnetic waves, magnetic fields or particles, optical fields orparticles, or any combination thereof.

Those of skill would further appreciate that the various illustrativelogical blocks, modules, circuits, and algorithm steps described inconnection with the embodiments disclosed herein may be implemented aselectronic hardware, computer software, or combinations of both. Toclearly illustrate this interchangeability of hardware and software,various illustrative components, blocks, modules, circuits, and stepshave been described above generally in terms of their functionality.Whether such functionality is implemented as hardware or softwaredepends upon the particular application and design constraints imposedon the overall system. Skilled artisans may implement the describedfunctionality in varying ways for each particular application, but suchimplementation decisions should not be interpreted as causing adeparture from the scope of the present invention.

The various illustrative logical blocks, modules, and circuits describedin connection with the embodiments disclosed herein may be implementedor performed with a general purpose processor, a digital signalprocessor (DSP), an application specific integrated circuit (ASIC), afield programmable gate array (FPGA) or other programmable logic device,discrete gate or transistor logic, discrete hardware components, or anycombination thereof designed to perform the functions described herein.A general purpose processor may be a microprocessor, but in thealternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

The steps of a method or algorithm described in connection with theembodiments disclosed herein may be embodied directly in hardware, in asoftware module executed by a processor, or in a combination of the two.A software module may reside in RAM memory, flash memory, ROM memory,EPROM memory, EEPROM memory, registers, hard disk, a removable disk, aCD-ROM, or any other form of storage medium known in the art. Anexemplary storage medium is coupled to the processor such that theprocessor can read information from, and write information to, thestorage medium. In the alternative, the storage medium may be integralto the processor. The processor and the storage medium may reside in anASIC. The ASIC may reside in a user terminal. In the alternative, theprocessor and the storage medium may reside as discrete components in auser terminal.

The previous description of the disclosed embodiments is provided toenable any person skilled in the art to make or use the presentinvention. Various modifications to these embodiments will be readilyapparent to those skilled in the art, and the generic principles definedherein may be applied to other embodiments without departing from thespirit or scope of the invention. Thus, the present invention is notintended to be limited to the embodiments shown herein but is to beaccorded the widest scope consistent with the principles and novelfeatures disclosed herein.

What is claimed is:
 1. A method for wireless communication, the methodcomprising: selecting, by a processor of a mobile station, a basestation from a set of base stations in an active set, the active setincluding a set of base stations currently in communication with themobile station; estimating a preferred data rate at which the mobilestation can receive a first data packet from the selected base station;transmitting, to the base station, a data rate message that includes arequest to send the first data packet at the estimated preferred datarate; and receiving a beginning portion of an output sequence from thebase station, the output sequence comprising a combination of a block ofinterleaved data symbols of the first data packet and a block ofinterleaved parity symbols for the first data packet in which theplurality of interleaved data symbols are located at the beginningportion of the output sequence and the plurality of interleaved paritysymbols are located at an end portion of the output sequence.
 2. Themethod of claim 1, further comprising: receiving a first segment of theend portion of the output sequence.
 3. The method of claim 2, furthercomprising: based at least in part on the first segment of the endportion of the output sequence, determining if the beginning portion ofthe output sequence is decodable before an arrival of a second segmentof the end portion of the output sequence.
 4. The method of claim 3,further comprising: upon determining the beginning portion of the outputsequence is decodable before the arrival of the second segment of theend portion of the output sequence, transmitting an acknowledgmentsignal to the base station; and receiving a beginning portion of asecond data packet based on the base station processing theacknowledgement signal.
 5. The method of claim 3, further comprising:upon determining the beginning portion of the output sequence is notdecodable before the arrival of the second segment of the end portion ofthe output sequence, transmitting a negative acknowledgment signal tothe base station; and receiving the second segment of the end portion ofthe output sequence.
 6. The method of claim 1, at least one segment ofthe end portion of the output sequence transmitted by the base stationperiodically at every fourth slot of a transmission channel.
 7. Themethod of claim 1, further comprising: monitoring the pilot signal ofeach base station maintained in the active set; and determining asignal-to-noise-and-interference ratio (SINR) of a pilot signal fromeach base station in the active set.
 8. The method of claim 7, furthercomprising: predicting a future value of the SINR for each base stationbased on the determined SINR for each base station, the base stationselected based on the base station having a favorable future value ofSINR among the predicted future values of SINR.
 9. The method of claim1, further comprising: identifying a lower bound estimate for an actualSINR of the base station in relation to a duration of the first datapacket; and determining a maximum data transmission rate that can besustained by the base station when the actual SINR matches the lowerbound estimate.
 10. An apparatus for wireless communication comprising:a memory; and a processor operably connected to the memory, wherein theprocessor is configured to: select a base station from a set of basestations in an active set, the active set including a set of basestations currently in communication with the apparatus; estimate apreferred data rate at which the apparatus can receive a first datapacket from the selected base station; transmit, to the base station, adata rate message that includes a request to send the first data packetat the estimated preferred data rate; and receive a beginning portion ofan output sequence from the base station, the output sequence comprisinga combination of a block of interleaved data symbols of the first datapacket and a block of interleaved parity symbols for the first datapacket in which the plurality of interleaved data symbols are located atthe beginning portion of the output sequence and the plurality ofinterleaved parity symbols are located at an end portion of the outputsequence.
 11. The apparatus of claim 10, the processor furtherconfigured to: receive a first segment of the end portion of the outputsequence.
 12. The apparatus of claim 11, the processor furtherconfigured to: based at least in part on the first segment of the endportion of the output sequence, determine if the beginning portion ofthe output sequence is decodable before an arrival of a second segmentof the end portion of the output sequence.
 13. The apparatus of claim12, the processor further configured to: upon determining the beginningportion of the output sequence is decodable before the arrival of thesecond segment of the end portion of the output sequence, transmit anacknowledgment signal to the base station; and receive a beginningportion of a second data packet based on the base station processing theacknowledgement signal.
 14. The apparatus of claim 12, the processorfurther configured to: upon determining the beginning portion of theoutput sequence is not decodable before the arrival of the secondsegment of the end portion of the output sequence, transmit a negativeacknowledgment signal to the base station; and receive the secondsegment of the end portion of the output sequence.
 15. The apparatus ofclaim 10, at least one segment of the end portion of the output sequencetransmitted by the base station periodically at every fourth slot of atransmission channel.
 16. The apparatus of claim 10, the processorfurther configured to: monitor the pilot signal of each base stationmaintained in the active set; and determine asignal-to-noise-and-interference ratio (SINR) of a pilot signal fromeach base station in the active set.
 17. The apparatus of claim 16, theprocessor further configured to: predict a future value of the SINR foreach base station based on the determined SINR for each base station,the base station selected based on the base station having a mostfavorable future value of SINR among the predicted future values ofSINR.
 18. The apparatus of claim 10, the processor further configuredto: identify a lower bound estimate for an actual SINR of the basestation in relation to a duration of the first data packet; anddetermine a maximum data transmission rate that can be sustained by thebase station when the actual SINR matches the lower bound estimate. 19.An apparatus for wireless communication comprising: means for selectinga base station from a set of base stations in an active set, the activeset including a set of base stations currently in communication with theapparatus; means for estimating a preferred data rate at which theapparatus can receive a first data packet from the selected basestation; means for transmitting, to the base station, a data ratemessage that includes a request to send the first data packet at theestimated preferred data rate; and means for receiving a beginningportion of an output sequence from the base station, the output sequencecomprising a combination of a block of interleaved data symbols of thefirst data packet and a block of interleaved parity symbols for thefirst data packet in which the plurality of interleaved data symbols arelocated at the beginning portion of the output sequence and theplurality of interleaved parity symbols are located at an end portion ofthe output sequence.
 20. A non-transitory computer-readable mediumprogrammed with a set of instructions, the instructions executable by aprocessor to: select, by a mobile station, a base station from a set ofbase stations in an active set, the active set including a set of basestations currently in communication with the mobile station; estimate apreferred data rate at which the mobile station can receive a first datapacket from the selected base station; transmit, to the base station, adata rate message that includes a request to send the first data packetat the estimated data rate; and receive a beginning portion of an outputsequence from the base station, the output sequence comprising acombination of a block of interleaved data symbols of the first datapacket and a block of interleaved parity symbols for the first datapacket in which the plurality of interleaved data symbols are located atthe beginning portion of the output sequence and the plurality ofinterleaved parity symbols are located at an end portion of the outputsequence.